Congratulations on your old mac! If you want GB, look for GB2 - anything newer will suck on the ibook g3. Look for the iLife05 DVD. It'll be on there. Go to the macintosh garden and have a look too. There is a lot of neat music production stuff over there and all for the right price. CubaseLE v1.07 is another good daw choice if you can find it and it will run on Tiger. Audacity is yet another good free supported daw for basic stuff - IIRC it does have a reverb plugin.
I assume you're using a digital AI to record your tracks? Something FW400 will be loads better as usb1.1 on the ibook is mind numbing-ly slow. I'm a fan of presonus gear but everyone has their favs. I think you'll be fine doing basic 2-4 track stuff. It'll be slower and real time FX/monitoring via the ibook is probably off the table, but it's totally doable and you'll adapt to its limitations - the nature of the beast and part of the fun I think in making great music. As a few have said already, many an artist has made great music on lesser gear than what you have right there.
Best of luck to you. Post the first tune you make on it for us to have a listen